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Responses of internal mammary artery graft flow to nitroprusside: a duplex Doppler study in hypertensive hearts
S Bosi1, C Guadagni, M Pretolani
1Divisione di Cardiologia, Ospedale S. Maria delle Croci, Ravenna, Italy.
Insights
Hypertensive patients with normal heart mass respond similarly to nitroprusside as healthy individuals. However, those with hypertrophic hearts show reduced coronary vasodilator response and are prone to flow reduction during hypotension.
Area of Science:
- Cardiovascular Physiology
- Medical Imaging
- Pharmacology
Background:
- Hypertension can lead to left ventricular hypertrophy, altering cardiac function.
- Internal mammary artery (IMA) grafts are crucial for coronary artery bypass surgery.
- Assessing coronary flow dynamics in hypertensive patients is vital for managing cardiovascular risk.
Purpose of the Study:
- To evaluate the response of internal mammary artery (IMA) blood flow to nitroprusside infusion in hypertensive patients.
- To compare IMA flow dynamics in normotensive individuals, hypertensive patients with normal left ventricular mass, and hypertensive patients with left ventricular hypertrophy.
Main Methods:
- Utilized high-frequency duplex Doppler ultrasound via a supraclavicular approach to monitor IMA graft flow.
- Studied 15 patients: 5 normotensive controls, 5 hypertensive with normal left ventricular mass, and 5 hypertensive with left ventricular hypertrophy.
- Measured IMA flow volume at baseline and during nitroprusside infusion, assessing peak and end-point flow relative to blood pressure changes.
Main Results:
- Nitroprusside infusion caused comparable flow-volume increases in controls and hypertensive patients with normal left ventricular mass.
- Hypertensive patients with left ventricular hypertrophy exhibited a minimal flow-volume increase (6%) during nitroprusside infusion.
- While controls and normotrophic hypertensives maintained baseline flow at lower blood pressures, hypertrophic hypertensives experienced a significant 23% decline in flow.
Conclusions:
- Hypertensive patients with normal left ventricular mass demonstrate preserved coronary vasodilator response to nitroprusside, similar to normotensives.
- Left ventricular hypertrophy in hypertensive patients is associated with a blunted vasodilator response and increased vulnerability to hypotension-induced coronary flow reduction.
- Duplex Doppler monitoring of IMA graft flow offers a non-invasive method for dynamic assessment of coronary flow patterns in these patient groups.
Objective:
To assess the response of internal mammary artery (IMA) flow of hypertensive hearts to nitroprusside infusion.
Methods:
Fifteen patients were studied with a high-frequency duplex Doppler probe from the supraclavicolar approach. All the patients had undergone coronary artery bypass surgery with an IMA graft into the left anterior descending artery. The investigated patients were normotensives (controls, n = 5) and hypertensive with a normal (group 1, n = 5) or a hypertrophic (group 2, n = 5) left ventricle. Values of the left ventricular mass index were 102 +/- 11 g/m2 in controls, 115 +/- 18 g/m2 in group 1 and 153 +/- 8 g/m2 in group 2. The IMA flow volume was studied at baseline and continuously during nitroprusside infusion. The arterial blood pressure was measured each minute by a cuff sphygmomanometer. In each patient we considered the peak flow volume (percentage increment from baseline) and the flow volume at the end point (the lowest tolerated diastolic blood pressure).
Results:
Nitroprusside infusion induced a comparable flow-volume increment in controls (38 +/- 27%) and in group 1 (24 +/- 11%). Conversely, the flow-volume increment was trivial in group 2 (6 +/- 6%). At the end point, the flow volume was similar to the baseline value in controls (with diastolic blood pressure 67 +/- 9 mmHg) and in group 1 (diastolic blood pressure 61 +/- 4 mmHg), whereas the flow volume declined significantly from baseline (by 23%) in group 2 at a perfusion pressure of 79 +/- 9 mmHg.
Conclusion:
Hypertensive patients with a normal left ventricular mass exhibit a coronary flow behaviour similar to that of normotensives in response to a nitroprusside infusion. Conversely, hypertrophic hypertensives show a blunted nitroprusside-induced coronary vasodilator response and are much more vulnerable to coronary flow reductions in the face of hypotension. This dynamic assessment of flow patterns can be obtained non-invasively by duplex Doppler monitoring of IMA graft flow.